The role of lipid intermediates in the biosynthesis of the carbohydrate units of thyroglobulin is being investigated. A polar C14-labeled oligosaccharide-lipid soluble in chloroform-methanol-water, 10:10:3, has been isolated after incubation of thyroid particles with GDP-mannose or UDP-glucose or incubation of thyroid slices with mannose or glucose. Unlabeled lipid-oligosaccharide has also been isolated from calf thyroid glands. The carbohydrate portion of this lipid which contains mannose, glucose, and N-acetylglucosamine, has been shown to have a molecular weight of about 2500 and to be linked to the lipid by a pyrophosphate band. The structure of the oligosaccharide is being studies with the use of glycosidase digestion, periodate oxidation and acetolysis to determine the position and linkage of the various sugars. Incubations of the C14-labeled oligosaccharide-lipid with thyroid particle fractions are being performed to elucidate the steps in the transfer of the carbohydrate unit to protein acceptors. BIBLIOGRAPHIC REFERENCE: Spiro, M. J and Spiro, R. G., Lipid-saccharide intermediates in thyroid glycoprotein biosynthesis, in Proceedings of the Seventh International Thyroid Conference, Excerpta Medica, in press.